// 核心余元层面，只有一个字符串类型：字符串切片str或&str
//

pub fn string_contact() {
    let mut s1 = String::from("s1");
    let mut s2 = String::from("s2");
    s1.push_str(&mut s2);
    s2.push_str("sss2");
    println!("{}", s1);
}

pub fn ss(){}
